Can you get pregnant if you have intercourse four days before your first day of ovulation

ANY time there is penile insertion there is the risk of pregnancy.

Yes. Like Scott said, any time penis enters vagina, pregnancy is possible.

Some women have gotten pregnant while on their period.

Yes, actually 4 days is a good time for it. Since it takes time for sperm to travel.

How do you know your actual ovulation time, thiings like those phone apps don't really work